Can a family member sue you for a debt that is now over 15 years old? What about if she does not even have anything signed saying that I would pay her back. This family member is saying that she is talking to a lawyer about suing me for the amount I owe her and interest up to today.

Without a signed agreement I don't see how she can prove that she gave you any money.

With no sign documentation, it makes her case very hard to prove.

And even if she does prove you owe her the money, there is a statute of limitations (SOL). It is usually about 6 years depending on where you live. Therefore no court will allow her to procedure with the lawsuit if you file a defence of the SOL is out of date.

She either does not know the law (hence talking to a lawyer) or does know it and is just trying to scare you.

If she goes to a lawyer, she will be shown the door very quickly.

However, there is a question of ethics here. Did you actually borrow money from her with a promise to pay it back?